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A transient, one-dimensional lean NOx trap (LNT) model is described and implemented for vehicle systems simulations. The model accounts for conservation of chemical species and thermal energy, and includes the effects of O₂ storage and NOx storage (in the form of nitrites and nitrates). Nitrites and nitrates are formed by diffusion of NO and NO₂, respectively, into sorbent particles, and reaction rates are controlled by chemical kinetics and solid-phase diffusion. The model also accounts for thermal aging and sulfation by means of empirical correlations, which have been derived from laboratory experiments. Example simulation results using the Powertrain Systems Analysis Toolkit (PSAT) are presented.

We consider the effect of intra-channel mass and heat transfer in modeling the performance of diesel oxidation catalysts. Many modeling studies have assumed that the intra-channel flow is laminar and, thus, heat and mass transfer between the bulk gas and wall are appropriately described using correlations for fully-developed laminar flow. However, recent experimental measurements of CO and hydrocarbon oxidation in diesel exhaust reveal that actual mass-transfer rates can deviate significantly from those predicted by such correlations. In particular, it is apparent that there is a significant dependence of the limiting mass-transfer rate on the channel Reynolds number. Other studies in the literature have revealed similar behavior for heat transfer. We speculate that this Reynolds number dependence results from boundary-layer disturbances associated with washcoat surface roughness and/or porosity.